The present invention relates generally to a valve opening arrangement and method and, more particularly, to a valve opening arrangement and method including a yoke for moving one or both of two valves.
In many engines today, each cylinder is provided with two intake and two exhaust valves. The valves are often opened by a yoke connected to the two intake or exhaust valves. The yoke is generally forced in one direction to open the valves by a rocker arm and, usually, springs urge the valves to a closed position after the rocker arm force is released. The architecture of many engines places the valve yoke in close proximity to the rocker arm pivot shaft. This creates packaging issues that prevent the use of state of the art single-valve engine brake actuation. It is desirable to actuate only the valve closest to the rocker shaft to better utilize rocker arm mechanical advantage and allow higher cylinder pressures for more braking power. While this might be accomplished with a hydraulic lash adjuster that actuates through the valve yoke on the inboard valve, the proximity of the yoke to the rocker shaft on group engines does not leave any space to include this piston. Thus, the lash adjustment must be made to the entire yoke so that both valves are actuated under braking. This requires lower pressures for the given valve train package.
It is desirable to provide a valve opening arrangement that can provide for flexible valve actuation arrangements while occupying minimal space. It is also desirable to provide such a valve opening arrangement that facilitates both single valve actuation during engine braking and two valve actuation during engine exhaust.
In accordance with an aspect of the present invention, a valve opening arrangement comprises a first contact surface on a first member, a second contact surface on a second member discrete from the first member, a first and a second opening, a first and a second valve movable to open and close the first and second opening, respectively, and a yoke arranged to move the first valve and not the second valve when contacted by the first contact surface and arranged to move the first valve and the second valve when contacted by the second contact surface.
In accordance with another aspect of the present invention, a method of actuating exhaust valves in an engine is provided. The engine comprises at least one cylinder, the cylinder comprising first and second exhaust valves. In the method, a first contact surface on a first member is moved to a first valve open position in which the first contact surface contacts a yoke and thereby moves the first valve and not the second valve to an open position. A second contact surface on a second member is moved to a second valve open position in which the second contact surface contacts the yoke and thereby moves the first valve and the second valve to the open position, the first and second members being discrete from each other.